Nitrobenzene is one of the most important industrial chemicals with an annual global production of more than 2 million tonnes. In the USA alone, in 2001 more than 1.5 million tonnes of nitrobenzene were synthesized and the production since 1990 was more than doubled. In Germany, for example, in the Uerdingen Bayer works, there is a nitrobenzene plant having a production capacity of approximately 300 000 tonnes per annum; see press information Bayer AG, 30.01.2002. About 97% of the nitrobenzene produced globally is used for the production of aniline.
Nitrobenzene is synthesized by nitrating benzene using “nitrating acid” (HNO3+H2SO4). Approximately 0.1% of the benzene consumed arises as a result of the synthesis in the form of byproducts and thus as production wastewater. This wastewater contains, as main components, 2,4-dinitrophenol and picric acid (2,4,6-trinitrophenol) and also customarily a high loading of nitrogenous and sulfur salts; see Rajan J., R. Perkins and S. Sariaslani 1994, “Microbial degradation of picric acid”, Abstr. Q-121, p. 409. Abstr. 94th Ann. Meet. Am. Soc. Microbiol. 1994, and also Patil S. S. and V. M. Shinde, “Gas chromatographic studies on the biodegradation of nitrobenzene and 2,4-dinitrophenol in the nitrobenzene plant wastewater”, Environ. Pollut. 57, 1989, 235-250.
Nitrophenol compounds have a high toxic potential. This applies in particular to 2,4-dinitrophenol, the main impurity of the wastewaters customarily occurring in the production of nitrobenzene, particularly because of its decoupling action on respiratory chain phosphorylation; see Pinchot G. B., “The mechanism of uncoupling of oxidative phosphorylation by 2,4-dinitro-phenol”, J. Biol. Chem. 242, 1967, 4577-4583. Therefore, the synthesis wastewaters which occur must be fed to appropriate disposal methods. Currently four methods are used for this:                (a) the Deep Sea Dumping Method in which the problem materials are finally deposited in the deep sea,        (b) the Deep Well Injection Method, in which the wastes are fed by an injection method to sites in deep layers in the earth where they are not a hazard to groundwater,        (c) the thermolysis method in which the wastewater is thermally decomposed at approximately 280° C. at high pressure (see U.S. Pat. No. 5,232,605), and        (d) the ozonation method in which the wastewater is treated with ozone at temperatures between 60 and 100° C. under elevated pressure (see U.S. Pat. No. 6,245,242).        
However, in the Deep Sea Dumping Method and the Deep Well Injection Method, the wastes are merely finally deposited. In contrast, although the thermolysis method and the ozonation method are efficient in the disposal result, because of the necessary process procedure (temperature, pressure, use of ozone) they represent an immense cost factor within the overall nitrobenzene production method. In the thermolysis method, in addition it requires additionally increased safety precautions.